John Green wrote:
I read that Phrack article and their jammer is much more sophisticated than mine. Mine is just a sweeper. I don't even know yet the sweep rate. I was thinking more along the lines of theirs. Something that actually put out a signal that contained at least some aspects of the signal they were intending to jam. My next experiment will be to get a clock oscillator that works at some submultiple of the GPS frequency and see if one of its harmonics can jam a handheld GPS if held close by.
Yes, it will.. It doesn't even have to be a submultiple. Most GPS receivers have a pretty wideband front end filter feeding a single bit ADC. Why a wideband filter? Because it's hard to make a 1 MHz wide filter at 1500 MHz that is temperature stable. Much easier to make a 10,15,20 MHz wide filter (1-2% bandwidth) and let it move around. So, I would venture that ANY signal within a few MHz of the GPS center at 1575 would jam it.
Bear in mind that if you are doing a comb generator, the power in each comb spur is pretty small. 1 mW at 10 MHz with harmonics up to 2 GHz means you're spreading that mW over 200 teeth of the comb, so each one is -23dBm.
For more jamming fun.. What about a 200kHz spacing comb mixed with a FM modulated carrier at, say, 99.9 MHz... Enjoy..
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